Polyols, such as glycerol, erythritol, xylitol and sorbitol, undergo hydrogenolysis in the presence of a hydrogenation catalyst and an inorganic hydroxide base to yield, primarily, glycerol, ethanediol and 1,2-propanediol. Other products may include tetritols, lactic acid, methanol, ethanol and propanol. Xylitol and sorbitol are available from biomass, such as forest and agricultural products, from which cellulose and hemicellulose can be extracted, hydrolyzed and reduced to these polyols.
Until recently, it was considered that the most economically rewarding product of the hydrogenolysis of polyols was glycerol, and that ethanediol, hereinafter referred to as ethylene glycol, could be produced more economically from other hydrocarbon sources, in particular, petroleum sources. Now, due to the scarcity and expense of petroleum, an alternate route to ethylene glycol utilizing renewable and less costly resources is desirable.
The following references provide further background information.
U.S. Pat. No. 2,965,679 discloses hydrogenolysis of polyols at 200.degree. to 300.degree. C., 500 to 1,000 atm (50 to 101 MPa) and pH 8 to 10. The pH may be attained by the addition of calcium hydroxide.
U.S. Pat. No. 3,030,429 discloses hydrogenolysis of sorbitol and mannitol at 180.degree. to 250.degree. C., up to 1,000 atm (101 MPa) and pH 11 to 12.5. The pH may be attained by the addition of calcium hydroxide.
U.S. Pat. No. 2,852,570 discloses a process for the hydrogenolysis of hexites, e.g., sorbitol, to glycerol and ethylene glycol in the presence of a catalyst which contains only cobalt and nickel in addition to a carrier, e.g., alkaline earth oxides, at 200.degree. to 220.degree. C. and 100 to 200 atm (10 to 20 MPa). The catalyst, added in amounts of, e.g., 50 weight percent based on sorbitol, comprises, e.g., 75 percent magnesium oxide.
U.S. Pat. No. 2,325,207 discloses hydrogenolysis of carbohydrates and polyols in the presence of 5 to 7 weight percent of a catalyst comprised of a copper hydroxide and an iron and/or magnesium hydroxide, at 150.degree. to 250.degree. C. in an alkaline environment which can be achieved by the addition of an excess of alkali, e.g., sodium hydroxide in the amount required to neutralize initial acidity and to coprecipitate the hydroxides, plus 2 to 15 weight percent, based on substrate.
U.S. Pat. No. 2,004,135 discloses hydrogenolysis of polyols in the presence of an amount of a weakly alkaline buffer sufficient to maintain a weakly alkaline reaction mixture, preferably calcium carbonate although aluminum hydroxide is noted as useful, at 200.degree. to 300.degree. C., preferably 250.degree. C., and 1000 to 4500 psi (7 to 31 MPa).
U.S. Pat. No. 1,963,997 discloses hydrogenolysis of polyols at 100.degree. to 300.degree. C. and, e.g., 3000 psi (21 MPa) using a catalyst "containing a hydrogenating and a dehydrating component", e.g., nickel-chromium oxide.
U.S. Pat. No. 3,396,199 discloses hydrogenolysis of sugars in the presence of an alkaline earth metal oxide, hydroxide or weak acid salt in proportion to furnish from 0.25 to 1.0 weight percent of calcium oxide equivalent, based on the weight of substrate, at 190.degree. to 230.degree. C. and at least 500 psi (3.5 MPa).
U.S.S.R. Pat. No. 422,718 discloses hydrogenolysis of sugars at 235.degree. C. and 100 to 150 atm (10 to 15 MPa), with stirring, in the presence of, e.g., 2.5 weight percent of calcium hydroxide, 2.5 weight percent of ferric chloride hexahydrate and 8 percent nickel on kieselghur, based on substrate.
Balandin, A. A., et al., Uzbekskii khimicheskii zhurnal, Vol. 6, pp. 64-72 (1962), discloses a process for the hydrogenolysis of xylitol in the presence of 1 weight percent of calcium oxide, based on xylitol, at 200.degree. to 230.degree. C. and 200 atm (20 MPa).
Vasyunina, N. A., et al., Kinetika i Kataliz, 4, 156-162 and 433-449 (1963) disclose experiments designed to determine the effects of calcium oxide, barium oxide and sodium hydroxide, and the effects of temperature (200.degree. to 245.degree. C.) and pressure (100 to 250 atm) (10 to 25 MPa), on hydrogenolysis of xylitol.
Clark, I. T., Industrial Engineering Chemistry, Vol. 50, pp. 1125-1126 (1958), discloses hydrogenolysis of sorbitol in the presence of up to 3 weight percent of calcium hydroxide, based on sorbitol, at 215.degree. to 245.degree. C. and up to 5600 psi (39 MPa).
van Ling, G. and Vlugter, J. C., Journal of Applied Chemistry, Vol. 19, pp. 43-45 (1969), discloses hydrogenolysis of saccharides and hexitols in the presence of up to 5 weight percent of calcium hydroxide, based on substrate, at 200.degree. to 250.degree. C. and 100 and 300 atm (10 to 30 MPa).
Vasyunina, N. A., et al., Proc. Academy of Sciences USSR, Chemistry Section, Vol. 169, Nos. 4-6, 767-769 (1966), discloses hydrogenolysis of monosaccharides and polyols in the presence of various inorganic hydroxide bases, carbonates of calcium, barium and sodium, acetates of calcium and barium and certain nitrogen-containing bases at pH 7.5 to 8.5, at 230.degree. C. and 200 atm (20 MPa).
Poletaeva, T. I., et al., Bull. Academy of Science USSR, Division of Chemical Science, June 10, 1977, 2412-2414, discloses hydrogenolysis of glucose using Ni-Al.sub.2 O.sub.3 catalysts at 215.degree. to 240.degree. C. and 120 atm (12 MPa) in the presence of 3 to 3.7 percent of calcium hydroxide based on the weight of glucose.
Heretofore, studies into the hydrogenolysis of polyols have been directed predominantly to reactions carried out in aqueous solutions. This fact is illustrated by the observation that of the above references, only three suggest the use of nonaqueous solvents. These are U.S. Pat. Nos. 2,004,135, 1,963,997 and 3,396,199.
It is an object of this invention to provide a catalytic process for the hydrogenolysis of polyols in nonaqueous solvents, which process results in high conversion of the polyols to useful products, particularly ethylene glycol. It is also an object to provide such a process in which the solvent is a C.sub.1-4 monohydric alcohol, particularly methanol and ethanol.
The above objects are achieved by the use of large amounts of a base and by use of high temperature in nonaqueous solvents.